Definition and Application
The temperature of the viscous flow occurs after melting of the non-crystalline highlighter. The viscosity temperature is also the transition temperature of the non-crystalline high polymer from the high elastic to the viscous flow, which is the lowest temperature of such a high polymer molding. This type of high polymer material may change its shape with only a viscous flow occurs. Therefore, the high and low temperature of the viscosity is very important for the molding processing of the high polymer material. The higher the temperature of the viscosity, the more it is not easy to process.
Measurement method
The temperature of the viscosity can be measured by the method of thermal-mechanical curve, differential heat analysis. However, it should be noted that when the viscosity temperature is used as a reference temperature of the machining temperature, the closer to the pressure when the pressure is measured, the better the pressure during processing.
Features
Almost all of the high polymers are processed by their viscosity, and due to most of the polymers entering the viscosity below 300 ° C. This is lower than the flow temperature of other materials. It has brought a lot of convenience to processing forming. In order to properly and effectively decreased. It is important to understand and master the temperature of the highlightest and viscous flow laws. This is also a reasonable design of the polymerization process and the polymer processing process. Products for obtaining good performance. It has important guiding significance to achieve high yield, quality and low consumption.
Affecting Factors
Factors affecting the temperature of the viscosity are mainly flexible (or rigid) of macromolecular chains. The greater the flexibility, the lower the temperature of the viscous flow; the greater the rigidity, the higher the temperature of the viscosity. Second, the average relative molecular mass of the high polymer, the larger the average relative molecular mass of the high polymer, the larger the molecular abrasion, and the relative displacement of the macromolecule is harvened, and therefore, the temperature of the viscosity is higher.
Molecular Structure Factor
Since the viscous flow is a change in the relative position between the molecules, when the molecular sense is large, it must be able to overcome the molecule at a higher temperature. The interaction flows to achieve a change in relative positions, so the polarity of polarity necessarily has a higher viscosity temperature. E.g. Polar effects of polyacrylonitrile as high molecules. The strength is strong, so that its viscosity temperature is far from its decomposition temperature. It is actually impossible to achieve flow. Therefore, the polyacrylonitrile fibers cannot be melt spinning. Solution can only be spinned. PVC is also strong due to molecular weight. The viscosity temperature has exceeded its start decomposition temperature, so a sufficient amount of stabilizers must be added during processing to increase its decomposition temperature.
The rigidity of the molecular chain is bigger. The higher the temperature of the viscosity. This is due to the greater the rigidity, the longer of the free movement, the longevity of the long segment needs to be larger, and only the high temperature may cause a large hole. Typical rigid molecules such as polyphenylene ether, polysulfone, etc. have a relatively high viscous flow temperature. Some strong rigid polymers such as polyazurine amines are difficult to mold due to too high of the viscosity, and must be modified. The temperature of the viscosity is high and indicates the high softening point. For plastic, the temperature of the viscosity is high, and its heat-resistant deformation is good.
Relative molecular mass
The higher the mass mass, the higher the temperature of the viscous flow. Because of the molecular chain length, the internal friction resistance is large (physical entanglement), and the disorderly thermal motion of the chain itself prevents the entire molecular chain to move towards a direction. Therefore, a higher temperature can cause relative displacement of molecules. . From processing molding, it is not desirable to have a relatively molecular mass, otherwise it will affect product quality due to high processing temperatures. In addition, the relative molecular mass distribution has an effect on the temperature of the viscous flow.
External force Factors
Increased external force can promote the effective displacement of the molecular chain, and partially cancel the segment disorderly motion, which is advantageous to relieve physical entanglement, thereby lowing the temperature. This principle is often used in actual production. For example, a resin having a high viscosity temperature and a large viscosity. In its injection molding, a large injection force is often used for cooling molding. Extend the force time. It is also possible to promote molecular center of gravity displacement and reduce the temperature of the viscous flow. The so-called cold flow phenomenon is the displacement of the molecular chain under the long-term effect of the polymer material in the long - gravity of its own gravity.
The high polymer's viscosity is the lower limit temperature of the molding, but the temperature is too high, the liquidity is too liquid, and the trouble and product shrinkage rate of the process will be excessive. It is particularly serious. Resin decomposition directly affects the quality of the molded articles, so the formation of the formation of the high polymer must be between the temperature of the viscosity and the decomposition temperature. The temperature and decomposition temperature of the viscosity and the decomposition temperature are so good to shape the processing.